Nope. The second and third x16 slots only run @ x4 and x1 speed, and SLI requires that all slots that are used for SLI be at least x8 speed.
So yes, it's Crossfire capable (because slot speed doesn't matter for Crossfire), but not SLI capable.
I'm pretty sure that there aren't any H77/B75 boards that are SLI capable.
As far as AMD cards go, something in the 6870 and above and 7850 and above range are good. You can Crossfire with lesser cards, but at that point, it's just better to get a single strong card.
Ugh... Great now I can't SLI the 570... Either have to get a new Nvidia Card or get two cheaper Radeon cards.